THE ANNALS OF „DUNAREA DE JOS” UNIVERSITY OF GALATI

FASCICLE XIV MECHANICAL ENGINEERING, ISSN 1224-5615

2009

61

SPECIFIC ASPECTS OF MODELLING AND

DESIGNING GEAR PUMPS

Assoc. ec. dr. eng. Adrian Mihai GOANTA

University “Dunarea de Jos” of Galati,

Research Center for Mechanics of the Machines

and Technological Equipments

ABSTRACT

The paper intends to highlight, in the context of general geometrical modelling, the

specific aspects of design and modelling of a gear pump. In practice in such

situations containing toothed gear it is recommended to use specific subroutines

that are able to access library data bases.

KEYWORDS: CAD/CAE, Autodesk Mechanical Desktop 2008

1. Introduction CAD - Computer Aided Design is now

increasingly used in the various fields of mechanical

engineering, architecture or product design, being a

rapidly developing field. The modern design

assistance is no longer limited only to the systems

simple drawings using the computer, followed by

placement of sizes and shades, but have evolved by

adding features and new instruments for 3D

modelling, with the possibility of creating solid

models and geometric surfaces, based on the

parameters specified by the design engineer.

The design is an iterative process and

consists of several phases, some wider, some more

diminished. These phases are:

� Comparative study –allows to identify the shortcomings of the already designed products

and it is carried out by an experienced engineer

that concludes whether launching a new

product is convenient

� Defining functions refer to determining both the main function and the secondary ones the

and grouping them into a specification of the

product to be designed. Specification includes

the physical and functional features , cost,

quantity and operating performance

� Synthesis and analysis are relatively interlinked and are contained into an iterative process. A

particular component of a comprehensive

system is conceived by the designer, analyzed,

and improved through analysis and redesign.

This process is repeated until the project is

optimized under the constraints imposed by the

designer. Components and subsystems are

summarized in the global system in a similar

way

� Evaluation refers to the degree of meeting the conditions set out in the specification established in

the problem definition phase. This assessment

often requires the manufacture and testing of a

prototype model to obtain data on performance,

quality and profitability;

� Presentation is the final phase of the project and includes the necessary documentation,

namely the project execution drawings, specifications

of materials, parts lists, etc..

With this type of pump and engines the

transmission of pressurized fluid between suction

and discharge is performed by the gaps between the

pin teeth, the housing and side covers, the fluid

circulation in the pump, between suction and

discharge taking place as shown by the arrows in

Figure 1.

Aspiration is determined by the depression that

arises at the gear teeth outlet in the suction area, fluid

is discharged at the gear teeth inlet in area R. The

efficiency of transport is influenced by the radial

clearance between the teeth and the outer housing, as

well as by the axial clearance on the front surface

between gears and side covers. Transmission is

provided by the upper pins, which, through the gear,

causes the bottom gear to move as well.

Due to the existence of two zones with

different pressures, low pressure suction A and high

pressure discharge R, a strong imbalance of forces in

the static pump (and engine) occurs the resultant

being directed from R to A

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Figure 1. Sketch of the external oil gear : 1- leading

gear ; 2-led gear ; 3-lathing ; A-suction space; R-

discharge space

2. Theoretical Aspects of Mechanical

Desktop Design Three-dimensional modelling of the oil

pump from Dacia 1310 underlines the benefits of 3D

design using one of the most used software packages

produced by Autodesk Inc. namely: Autodesk

Mechanical Desktop 2008. Assembly generating

starts from the creation of each item of the pump,

namely: pins, lower body containing pin box and oil

propulsion groove/channel , the upper body or sieve ,

shaft, arch and ball, holding screws, nuts and the

sieve which draws the oil from the bath oil.

Parameterization of each item is based on

the working plan "Work features / Work Plan" in

the "Part Modelling menu , drawing the profile

sketch, add profile to the work plan, applying the

constraints and sizing the profile by introducing the

actual dimensions. Perhaps the biggest advantage of

parameterized modelling is to save precious time to

generate views and sections. Thus, for the three

projections of a particular item, open the "Drawing

layout, select the" Multi-views”, then choose the type

of view you want to do , select the plan from which

we look, return to format layout and using the

mouse position the 3 projections, and the axonometric

view . Autodesk Mechanical Desktop 2008 includes

tools for sizing pieces (which can be parameterized

and defining a size can be done by equation) and also

for the drawing annotations, tables etc. for holes, all

these being changed automatically according to

changes made in the part geometry.

Automatic generation of design and

execution and bidirectional association along with the

3D model is one of the most important features of the

software used. Projections are generated in "Paper

Space" and can be of the following types: base,

orthographic, isometric, auxiliary, partially sectional,

full sectional, sectional offset, iso-sectional, detail,

user-defined.

Any change in the three-dimensional model

will be reflected in the design and execution, as any

change of size will lead to changes in the model

3. Generating Gears Teeth The gear teeth can be generated by the

following two methods:

- Manual method, which involves defining an involutes arc with the size resulted from an

engineering calculation, corresponding to the

tooth flank, an arc which multiplied polar around

an axis of rotation and completed with circle arcs

delimiting the head and foot of the tooth lead to

a final sketch of the front tooth, by extrusion this

further generating the 3D model of the gear.

Mention must be made that this method is

recommended for experts in designing and

generation, who master very well the technique

of engineering calculation and subroutines

AutoLISP for the generation of involutes type

curves.

Figure 2. Launching command “Shaft Generator”

THE ANNALS OF “DUNAREA DE JOS” UNIVERSITY OF GALATI FASCICLE XIV

63

Figure 3. “Shaft Generator” Window

Figure 4. Gear generating parameter window

- Automatic method of generating gears by command "Shaft Generator" from "Content 3D"

menu - as shown in Figure 2, which involves

opening a generating window title " 3D Shaft

Generator " - Figure 3 where option "Gear"

generation” will be chosen.

Figure 5. Toothed gear obtained by “Shaft Generator”

This option will open a new window shown

in Figure 4, where the designer must define all the

numerical values of the requested geometric

parameters. The result of the gear generation

subroutine is presented in Figure 5.

Figure 6. Leading shaft

Similarly, the pair of toothed gear was made,

having the role of a leading wheel. It should be noted

that it must be keep in mind that both toothed gears

have the same module and their external diameter

should be taken as a parameter in the pump body

design draft/sketch, for the cell generation where the

pair wheels would spin. Also in case of the leading

gear , by means of command "Shaft Generator" it

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was generated the cylindrical portion of the rod and

the groove at the rod end which takes the rotation

torque. The groove library contains both grooves as

such and various profiles, standardized or not, that

can be used by the designer to complete the end of a

shaft.

4. Generating the Toothed Gear Pump

After the two toothed gears were modelled, each item

can be modelled and in the end the related model can

be generated taking into account the 3D restrictions of

the adjoining pieces. For a better visualization, in

Figure 7 there were assigned glass properties to those

components that cover the gear. It should be noted

that the items of body and cover types are

characterized by a remarkable complexity of

geometric forms.

Figura 7. Model related to the gear pump assembly

5. Conclusions After completion of the design process, it is

important to transmit accurately the design parts

information to the teams responsible to order and

manufacture the product. If a general software design

is used, this operation often involves the manual

creation of tables and lists of materials (BOMs). Even

in the case of the smallest changes in design, the

manual methods can introduce critical errors that

could lead to delays in its delivery to the customer.

To prevent errors and costly delays, Autodesk

Mechanical Desktop 2008 offers the possibility of

making up a list of materials (BOM) integrated into

normal work flow so that the component table and the

BOM contain information on the component parts,

the whole information being updated as soon as a

change in design is made. These accurate data allow

designers to work more effectively with other

departments and suppliers.

References [1] Axinti, A.S., Nastac, S. * * * Introduction to Hydraulic and

Pneumatic Drives Theory – Impuls Publishing House, 2006,

BUCURESTI; ISBN (10) 973-8132-58-4; ISBN (13) 978-973-

8132-58-0; [2] Axinti, G., Axinti, A.S. Drives of hydraulic and pneumatic –

Dynamically of the equipments and of the systems – vol. II.

Tehnica-Info Publishing House, Chişinău-2008, ISBN-978-9975-910-85-9.

[3] Axinti, G., Axinti, A.S. The theory drives of hydraulic and

pneumatic – Components and systems, functions and features - vol

I. – Tehnica-Info Publishing House, Chişinău-2008, ISBN-978-9975-63-112-9;

[4] Goanţă, A. M. & Axinti A., Geometry stage 3D modelling of a heat station pump. Annals of “Dunarea de Jos” University

of Galati, Fascicle XIV, Mechanical Engineering, 2007, ISSN

1224-5615. pp. 48-51.

[5] Haraga G., Applications of CAD systems Proceedings of

The 3rd International Conference on Engineering Graphics and

Design, June 12-13, Cluj-Napoca, Romania pp.291-294.